Slides were often used at various times in history as jewellery accessories but there were two main types of slides. The first type, seen in the 17th and 18th centuries, were ornamental jewellery items used for bracelets and necklaces. These early slides usually had one or two bars at the back through which a ribbon could be threaded which enabled the ribbon to be adjusted without the use of a tongue or buckle to hold the ribbon firm. An example of such a slide is the one below. This is a piece of Stuart crystal (commemorating King Charles I, of the House of Stuart, who was executed in 1649). It is made of clear, faceted rock crystal, enclosing initials made from gold wire. The back is enclosed. It has two bars for a ribbon.
Slides also began to mean a piece of jewellery that held two strands of chain together but which can be slid up and down to lengthen or shorten the chain around the neck. This type of slide is associated with long guard or watch chains.
In the photo above, three slides, gold shapes with flower engravings, allow the user to alter the drape of the festoon necklace.
In this photo, a turned hollow gold slide allows the two chains holding the fob (in the shape of a horn) to be shortened or lengthened.
In this photo, a small gold square slide, inset with a tiny seed pearl, allows a guard chain length to be altered.
This final photo is of a commonly found slide with a central cameo. Slides are very versatile jewellery pieces. Some are enamelled, set with diamonds or pearls, engraved or inscribed. The size can differ a lot and they can be made of gold or be gold filled. You can find them sold separately and it is worthwhile looking out for them.